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introducing let-syntax

The let-syntax expander is different in that it doesn't apply
a mark to its token trees before expansion. This is used
for macro_rules, and it's because macro_rules is essentially
MTWT's let-syntax. You don't want to mark before expand sees
let-syntax, because there's no "after" syntax to mark again.

In some sense, the cleaner approach might be to introduce a new
AST node that macro_rules expands into; this would make it clearer
that the expansion of a macro is distinct from the addition of a
new macro binding.

This should work for now, though...
This commit is contained in:
John Clements 2014-07-07 09:54:08 -07:00
parent 92c2ff6d69
commit 9ee9c49cb4
3 changed files with 30 additions and 3 deletions

View file

@ -13,7 +13,7 @@
use lint::LintPassObject;
use syntax::ext::base::{SyntaxExtension, NamedSyntaxExtension, NormalTT};
use syntax::ext::base::{IdentTT, ItemDecorator, ItemModifier, BasicMacroExpander};
use syntax::ext::base::{IdentTT, LetSyntaxTT, ItemDecorator, ItemModifier, BasicMacroExpander};
use syntax::ext::base::{MacroExpanderFn};
use syntax::codemap::Span;
use syntax::parse::token;
@ -57,6 +57,8 @@ impl Registry {
IdentTT(ext, _) => IdentTT(ext, Some(self.krate_span)),
ItemDecorator(ext) => ItemDecorator(ext),
ItemModifier(ext) => ItemModifier(ext),
// there's probably a nicer way to signal this:
LetSyntaxTT(_, _) => fail!("can't register a new LetSyntax!"),
}));
}

View file

@ -264,8 +264,15 @@ pub enum SyntaxExtension {
/// A function-like syntax extension that has an extra ident before
/// the block.
///
/// `macro_rules!` is an `IdentTT`.
IdentTT(Box<IdentMacroExpander + 'static>, Option<Span>),
/// An ident macro that has two properties:
/// - it adds a macro definition to the environment, and
/// - the definition it adds doesn't introduce any new
/// identifiers.
///
/// `macro_rules!` is a LetSyntaxTT
LetSyntaxTT(Box<IdentMacroExpander + 'static>, Option<Span>),
}
pub type NamedSyntaxExtension = (Name, SyntaxExtension);
@ -300,7 +307,7 @@ pub fn syntax_expander_table() -> SyntaxEnv {
let mut syntax_expanders = SyntaxEnv::new();
syntax_expanders.insert(intern("macro_rules"),
IdentTT(box BasicIdentMacroExpander {
LetSyntaxTT(box BasicIdentMacroExpander {
expander: ext::tt::macro_rules::add_new_extension,
span: None,
},

View file

@ -484,6 +484,24 @@ fn expand_item_mac(it: Gc<ast::Item>, fld: &mut MacroExpander)
let marked_tts = mark_tts(tts.as_slice(), fm);
expander.expand(fld.cx, it.span, it.ident, marked_tts)
}
Some(&LetSyntaxTT(ref expander, span)) => {
if it.ident.name == parse::token::special_idents::invalid.name {
fld.cx.span_err(pth.span,
format!("macro {}! expects an ident argument",
extnamestr.get()).as_slice());
return SmallVector::zero();
}
fld.cx.bt_push(ExpnInfo {
call_site: it.span,
callee: NameAndSpan {
name: extnamestr.get().to_string(),
format: MacroBang,
span: span
}
});
// DON'T mark before expansion:
expander.expand(fld.cx, it.span, it.ident, tts)
}
_ => {
fld.cx.span_err(it.span,
format!("{}! is not legal in item position",